The present invention relates to a cutting bit, a cutting tool and a method for machining.
Similar cutting bits, cutting tools and a machining method for use therewith are described in German Patent Application No. 41 35 681 and the corresponding European Patent Application No. 542 026.
That publication describes an apparatus and a method for machining rotationally symmetrical work piece surfaces, wherein various cutting bits are arranged along a disc-shaped tool carrier and are engaged successively with the work piece for machining. Therein, final machining is in the form of a roughing-down and smoothing operation during which a cutting bit with a substantially zigzag main cutting edge, i.e. formed by projecting and recoiling sections of the cutting bit, is advanced firstly in a radial direction, and then in a roughing-down operation a certain layer thickness is taken off the work piece surface for machining, whereupon the tool is then moved axially in order to perform a smoothing operation by means of which fine machining is effected.
U.S. Pat. No. 4,867,616 discloses a cutting bit which has the basic form of a prism, comprising two substantially parallel top and bottom surfaces and four lateral surfaces substantially perpendicular to the top and bottom surfaces, wherein cutting edges are formed at the transition of the lateral surfaces to the top and bottom surfaces, and wherein those lateral surfaces are not even, and, in the plan view onto the top surface or bottom surface, has alternate projecting and recoiling sections, wherein effective sections of main cutting edges are formed in the region of the projecting sections, and wherein secondary cutting edges extend from the relatively projecting sections of the main cutting edges rearwardly along the recoiling sections at least by a predetermined insertion depth.
With that cutting bit, the secondary cutting edges are bent relative to the main cutting edges partially by 60xc2x0 and in the corner regions by 45xc2x0 Furthermore, the machining surfaces are formed by recesses which are associated individually with each section of main cutting edge, wherein in the central region of a main cutting edge an angle of between 62xc2x0 and 72xc2x0 results between the machining surface and the main free surface.
Corresponding cutting bits are mounted on a milling cutter in such a way that their main cutting edges slightly overlap, and the main cutting edges of a cutting bit alternatingly cover over the recoiling regions of a successive cutting bit, so that the secondary cutting edges only engage with the tool by way of their regions which are directly adjacent to the main cuts. A corresponding tool is provided exclusively for feed in a radial direction, for the purpose of milling grooves, or the like, in a tool, for example.
In the face of this prior art, the aim of the present invention is to create a cutting bit, a cutting tool, and a corresponding method for machining work pieces, wherein the cutting bit is intended to be fed not only radially but also axially during machining the work pieces, and wherein the corresponding work piece surfaces should be of good quality and efficiently produced, i.e. within strict tolerances.
The selection of special angles firstly permits a positive cutting geometry both during radial and axial feed to the work piece, and, additionally, the reaction forces occurring are kept relatively low, so that neatly defined work piece surfaces can be produced within strict tolerances.
The design of the cutting bit according to the invention enables the cutting bit to be inclined somewhat downwardly relative to the feed direction, wherein a free surface is prepared for improved radial feed of the cutting bit to the work tool or to the work piece surface for machining, on the one hand, whilst it is still possible to maintain a positive cutting edge geometry whereby the cutting forces occurring are reduced.
With respect to a corresponding tool, the problem forming the basis of the invention is solved in that in the tool a corresponding cutting bit is used, and in that the tool seat has a supporting surface for the top or bottom surface of the cutting bit, which is inclined such that it falls away at an angle of between 8xc2x0 and 12xc2x0 relative to the radial feed direction.
The corresponding method uses a cutting bit and a cutting tool of the afore-mentioned kind, wherein the radial feed of the cutting bit towards the work piece surface is such that the top and bottom surfaces are inclined such that they fall away to the front relative to that feed direction.
The terms, xe2x80x9cradial feed directionxe2x80x9d and xe2x80x9caxial directionxe2x80x9d refer herein, first and foremostly, to a work piece which is rotating about an axis, so that during machining a rotationally symmetrical surface is produced on that work piece. Therein, the feed generally takes place in such a way that the cutting edge and the axis of rotation of the rotating work piece lie in a common plane, and feed of the cutting bit also takes place exactly in that plane, initially in a radial direction. After the desired diameter of the rotationally symmetrical work piece has essentially been obtained, the cutting bit moves axially relative to the work piece for fine machining to ensue, and, in particular, the regions which initially were still remaining between the interrupted main cutting edges are removed by axial rotation.
However, the invention can be extended thoroughly to machining methods in which non-rotationally symmetrical surfaces, e.g. even surfaces, are machined, and the cutting bit is accordingly arranged on a rotating tool. In such a case, the terms, xe2x80x9cradial feedxe2x80x9d and xe2x80x9caxial feedxe2x80x9d are defined in relation to the axis of rotation of the tool.
According to the invention, the complementary angle cc between the machining surface and a plane which is perpendicular to the plane of the free surfaces of the main cutting edges is between 14 and 18xc2x0, and, with a preferred embodiment, it is 16xc2x0.
This means, for example, that in the case of the preferred embodiment mentioned latterly, the seating for the cutting bit, or the top and bottom surfaces of the cutting bit can be inclined at an angle of approximately 10xc2x0 relative to the feed direction, wherein a positive machining angle of approximately 6xc2x0 nonetheless remains in the region of the main cutting edge. The inclination of the top and bottom surfaces by approximately 10xc2x0 relative to the feed direction means at the same time that the plane of the free surfaces, which, due to the prismatic basic form of the cutting bit, extends substantially perpendicularly to the top and bottom surfaces, is likewise inclined by 10xc2x0 relative to a tangent on the work piece surface in the region of the active main cutting edge, so that an effective free angle of about 10xc2x0 is formed. It will be appreciated that in the case of a rotating work piece surface because of the curvature of the surface generated the free angle becomes increasingly larger directly behind the cutting edge.
This cutting geometry and arrangement of the cutting bit produce very small cutting forces so that harmful vibration of the work piece, such as can occur with different cutting edge geometries, is largely avoided. At the same time, wear to the cutting edge is reduced.
In addition, the geometry of the cutting bit which is actually selected enables main cutting edges 10 to be formed both at the transition of the respective lateral surface to the top surface as well as at the transition of that lateral surface to the bottom surface of the cutting bit. Therefore, after one of the main cutting edges of the cutting bit has become worn, the cutting bit can be turned and used again. This effect is rendered two-fold in a preferred embodiment of the invention wherein the cutting bit has the basic form of a cuboid with two shorter lateral surfaces and two longer lateral surfaces, wherein cutting edges are formed on each of two oppositely disposed lateral surfaces, and, to be more exact, at the transition to the top and bottom surface respectively, so that a total of four main cutting edges is formed which are interrupted main cutting edges corresponding to the projecting and recessed regions of the lateral surfaces and to which respective secondary cutting edges are adjacently disposed which extend at least a little way into the recessed regions of the lateral surfaces in question.
In this embodiment, there is a total of four cutting edges, each of which can be changed over after the cutting edges have become worn. This makes the cutting bit according to the invention very economical to use.
One embodiment of the invention is particularly preferred wherein the individual sections of the interrupted main cutting edge are main cutting edge sections lying on a common straight line. This facilitates the production of rotationally symmetrical surfaces.
In the preferred embodiment, the secondary cutting edges which are adjacent to the main cutting edge sections, should, in the plan view onto the top or bottom surface, be bent at an angle of between 65xc2x0 and 70xc2x0, in particular of 67.5xc2x0, relative to the main cutting edges. Therein, each of the main cutting edge sections should be delimited as symmetrically as possible on both sides of a corresponding secondary cutting edge. In this way, an axial smoothing movement in both directions is possible, which simplifies the corresponding machining methods.
Preferably, at least two projecting regions, and thus two main cutting edge sections, are provided 5 along the lateral surfaces concerned, these main cutting edge sections being interrupted by a recessed region, wherein secondary cutting edges extend from the ends of the main cutting edges into this recessed region. However, one embodiment of the invention is particularly preferred wherein a total of three projecting regions is provided, wherein one is provided centrally in the middle of the corresponding lateral surface and defines a centrally arranged main cutting edge, whilst the other two projecting regions are arranged in the vicinity of the oppositely disposed ends of that lateral surface, and form main cutting edge sections there which are delimited at the transition to the respective other lateral surfaces by relatively short secondary cutting edge sections, wherein the length of those secondary cutting edge sections is less than the depth of the recessed regions of the lateral surfaces.
One embodiment of the invention is particularly preferred wherein additional recesses in the machining surfaces are formed within the projecting regions, which recesses impart to the secondary cutting edges a positive cutting edge geometry during axial feed.
Furthermore, the angle formed between the secondary cutting edges and the main cutting edges, in conjunction with the free surfaces of the secondary cutting edges which are angled in the same way relative to the free surfaces of the main cutting edges, and in conjunction with the inclination of the cutting bit in the feed direction, during the axial feed causes the free surfaces of the secondary cutting edges to form a positive free angle with the work piece surfaces produced by the secondary cutting edges. This feature also reduces the axial cutting forces and feed forces which additionally helps towards smoother movement of the rotating work piece, or, in the case of a rotating tool, towards smoother movement of the tool, with the result that very high-quality surfaces can be produced by this kind of machining under conditions which are also very economical.
Expediently, a corresponding cutting bit has a central bore, the axis of which extends perpendicularly to the top and bottom surface. This bore can be tapered somewhat in the center of the cutting bit between the top and bottom surface, or, in the region of the top and bottom surface, it can define a seating of variable conicity for a tightening screw, so that the cutting bit can be fastened to an appropriate seating of an appropriate tool by the use of an appropriate tightening screw.
The geometry defined herein above of the cutting bit according to the invention also makes it possible advantageously and economically for the cutting bit to be able to be formed under compressive conditions which significantly reduces the production cost of such a cutting bit. At the same time, the cutting bit has a positive cutting geometry and a positive free angle, but nonetheless has cutting edges both at the top surface as well as at the bottom surface respectively, so that the cutting bit according to the invention combines excellent cutting properties with a very cost-effective method of manufacture, and, additionally, economical wear behavior.
The corresponding cutting tool is adapted to the cutting bit according to the invention, so that the seating for the cutting bit in that tool slopes relative to the feed direction of the tool at an angle of between 8 and 12xc2x0. In addition, the seating has a threaded bore for receiving a tensioning screw for fastening a corresponding cutting bit.
With the method according to the invention, preferred embodiments are characterized in that the angle of inclination of the top and bottom surfaces relative to the feed direction is within the range of 8 and 12xc2x0, wherein an angle of 10xc2x0 has proven to be expedient in practice.